1. Field of the Invention
The present invention relates to an image forming apparatus and more specifically, to an image forming apparatus that writes a drawing and erases a drawing by a laser light on a thermal rewritable recording medium.
2. Description of the Related Art
There is a case where a thermal paper is used for a label on which a name of an article or an address to send the article is printed. For example, such a label composed of the thermal paper is used for a plastic container at a factory. Such a label composed of the thermal paper has a property that its color changes by heat, and therefore, characters or symbols can be written on the label by a heating head or the like.
There has been developed a rewritable type where writing and erasing can be repeated for such a thermal paper. As for the label used for delivery, it is desirable to write and erase the information on the label while the label is kept attached to the container, therefore, a method by which characters are written on the label without contacting the label by emitting a laser light to heat the label has been proposed (for example, see Japanese Laid-open patent publication NO. 2004-90026). In Japanese Laid-open Patent Publication NO. 2004-90026, a writing apparatus including a relay lens composed of plural lenses and flexible joints where an image input to one end of the relay lens is output from the other end is disclosed.
As for such a label composed of the thermal paper of rewritable type (hereinafter referred to as “rewritable paper” as well) as described above is used, when rewriting a new content on the label, it is necessary to erase a content already written on the label before writing the new content on the label.
Japanese Laid-open Patent Publication NOs. 2007-216422, 2004-322493, 2009-172801 and 2008-194905 disclose methods for erasing the drawings such as characters or the like written on the thermal paper.
For example, there is disclosed in Japanese Laid-open Patent Publication NO. 2007-216422, a technique of erasing drawings of all the area of the thermal paper by blowing hot air onto all the area.
There is disclosed in Japanese Laid-open Patent Publication NO. 2004-322493, an apparatus for erasing drawings on the thermal medium by which light is condensed as a linear light and the light source is divided by shutters or the like to enable partial erasing on the thermal medium.
It is disclosed in Japanese Laid-open Patent Publication No. 2009-172801, that drawings on a thermal medium are erased by a laser beam the same as that used for writing drawings on the thermal medium without providing an additional device for erasing the drawings.
It is disclosed in Japanese Laid-open Patent Publication No. 2008-194905, that an area to be partially erased is extracted by comparing images and erased in a rewriting system using a laser apparatus for writing and a laser apparatus for erasing.
However, it takes time for rewriting according to the above described techniques. For example, when erasing all area of the label, it takes time for erasing. Further, according to the technique disclosed in Japanese Laid-open Patent Publication No. 2008-194905, the operation becomes complicated because it is necessary to compare images, which requires a long operational time. Further, an apparatus for obtaining the image is additionally required.